The menopause marks a period of critical change in women's biology and health status. Unlike puberty, no staging system for reproductive aging has been established. A staging system for reproductive aging would facilitate development of health interventions, enable providers to better counsel women about menopausal symptoms and preventative therapy, and permit researchers to better classify women's reproductive status. In July 2001, NIA and other organizations held a workshop to propose a staging system for reproductive aging (STRAW). Although STRAW's recommendations built upon emerging results from cohort studies of midlife women and represent an expert consensus, they were not database driven. STRAW's bleeding criteria for the early and late transition stages, although conceptually consistent with prior definitions, include important departures from current clinical and research practice. Also, STRAW did not provide unambiguous operational definitions for these bleeding criteria. The goal of this application is to empirically evaluate 5 proposed bleeding criteria for onset of the early menopausal transition and 4 proposed bleeding criteria for onset of the late transition that served as the basis for the STRAW recommendations. We will use menstrual calendar, hormone and symptom data accumulated from five of the large and comprehensive cohort studies of the menopausal transition (the Tremin Trust, Melbourne Women's Midlife Health Project, Seattle Midlife Women's Health Study, Michigan Bone Health Study and the multi-site, multi-ethnic Study of Women's Health Across the Nation). We propose to assess 1) how frequently each criterion is well defined (i.e., are we able to categorize women by reproductive stage using the criterion?), 2) whether the age at transition differs among the criteria within and across cohorts, 3) the relationship between age at transition and age at menopause, and 4) whether prediction of age at menopause is improved by including predictors such as FSH, or hot flash, and whether it varies by ethnicity, smoking status or body mass index. This study will provide empirical evidence regarding which criteria are broadly representative across populations and across the range of menopausal ages, furthering efforts to establish staging criteria for the menopausal transition. This information will help clarify our understanding of ovarian aging, permit researchers to more adequately control for menopausal status, and facilitate decision-making among women and their providers.